1. Field
Example embodiments of the present invention relate in general to the field of semiconductor devices and more specifically to light emitting diodes (LEDs).
2. Discussion of the Background
A light emitting diode (LED) is basically a PN junction diode including a junction between a P-type semiconductor and an N-type semiconductor.
In the LED, after the junction between the P-type semiconductor and the N-type semiconductor is formed, when a voltage is applied to the P-type semiconductor and the N-type semiconductor and a current flows, holes of the P-type semiconductor may move toward the N-type semiconductor, and electrons of the N-type semiconductor may move toward the P-type semiconductor, so the electrons and the holes may move to a PN junction portion.
The electrons, which have moved to the PN junction portion, may be dropped from a conduction band to a valence band and combined with the holes. In this case, energy corresponding to a height difference (i.e., energy difference) between the conduction band and the valence band may be emitted in the form of beams.
The LED is a light emitting semiconductor device, which may be environmentally friendly and characterized by a low voltage, a long lifespan, and a low price. Although conventional LEDs have mainly been applied to display lamps or devices configured to display simple information, such as numbers, the latest LEDs are being used in a wide variety of fields, such as displays, automobile head lamps, and projectors, with the development of industrial technology, particularly, the development of information display technology and semiconductor technology.
LEDs may include horizontal LEDs and vertical LEDs. A vertical LED exhibits better current dispersion performance than a horizontal LED. Also, the horizontal LED uses a growth substrate, such as a sapphire substrate, as a support substrate, while the vertical LED uses a substrate, such as a metal substrate having a high thermal conductivity, and exhibits excellent heat emission performance.
A method of fabricating the vertical LED includes growing a GaN epitaxial layer using a sapphire substrate, and isolating the GaN epitaxial layer from the sapphire substrate using a laser liftoff (LLO) process (Korean Patent Publication No. 2012-0099544).
When an epitaxial layer is grown on a heterogeneous substrate, such as a sapphire substrate, a lot of defects caused by a mismatch in a coefficient of thermal expansion and a lattice mismatch may occur in the epitaxial layer. Thus, there have been attempts to grow an epitaxial layer on a homogeneous substrate. However, since there is no or little difference in bandgap energy between the homogeneous substrate and the epitaxial layer, it is difficult to apply an LLO process to isolate the epitaxial layer from the substrate to fabricate a vertical LED.